This invention relates to surveying instruments and more particularly to an instrument for measuring the elevation of sewer pipes relative to manholes, to determine the flow line.
When surveying sewer lines, it is necessary to determine the elevation of the sewer pipes where they enter the box union. The vertical distance from the lowest point of the interior of the pipe, or "invert", to the upper edge of the manhole frame at the top of the box is currently measured by an awkward and labor intensive procedure. Surveying a sewer line requires making this measurement frequently at considerable cost. The measurement is critical in certifying that proper slope is maintained for drainage. Because the measurement is so awkward, it is subject to considerable error.